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True Cost of Wind Pumped Storage

By legislating pumped storage plants under House Bill 11-1083, the legislature has tripled the cost of wind energy development in Colorado.

State legislators took Colorado blindly down path of pumped storage without any consideration or anaylsis of the financial burden that their haste will bring  the citizens of Colorado. The proposed South Slope Pumped Storage plant for example, will increase the cost of  a 360MW wind project from $0.80 billion, up to $2.44 billion. Let's take a look at the math... 

Proponents state as fact, that pumped storage is essential to wind energy development in Colorado.  They expect us to accept this supposition while  conveniently leaving out the costs of tying pumped storage to wind energy expansion.

Before we do the arithmetic, it is key to understand "capacity factor". All power plants have a capacity factor, which tells you what percentage of the plant's maximum power can typically be produced in a given time period. For example: A 1000MW generating plant could in theory produce 24,000MWhrs of energy in a day (1000MW x 24hours). However, certain inherent characteristics might limit that generator to 60% of its full power over the day. Such a generator plant would have a capacity factor of 0.60, producing 14,400MWhrs of energy (24,000MWhrs x 0.60) in one day.

Another important concept is pumped storage efficiency. A pump storage plant with 75% efficiency that consumes 4,000MWhrs of energy filling the upper reservoir, would return only 3,000MWhrs  (4,000MWhrs x 0.75) of energy back to the grid after storage.

The South Slope Pumped Storage (SSPS) plant's developer submitted the following specifications in their FERC filing:

Plant Output Power = 432MW.    Full output utilization = 6 hours per day

Using a typical capacity factor of 0.30 for wind generators,  pumped storage efficiency of 75%,  and a 2008 wind plant construction cost of $2,250 per KW, we can calculate the development cost of wind energy coupled with pumped storage:

 1. Daily Output Energy of SPSS to Grid = 2,593MWhrs    (432MW x 6hours)

 2. Daily Input Wind Energy used by SPSS = 3457MWhrs    (2,593MWhrs / 0.75)

 3. Input Wind Power needed by SPSS  = 192MW   (3457MWhrs / (24hrs - 6hrs) )

 4. Required Wind Plant Power = 640MW   (192MW / 0.30)

 5. Build Cost of Wind Power = $1.44 billion   (640MW x ($2,250,000 per MW) )

 6. Cost of Pumped Storage = $1 billion

Total cost for building the capacity to produce 2,593MWhrs of wind energy per day, with pumped storage = $2.44 billion.


We can also calculate the cost of developing the same amount of energy capacity using wind power connected directly to a balanced grid, without pumped storage.

 1. Daily Direct Output Energy to Grid = 2,593MWhrs  (same as SPSS daily output)

 2. Required Wind Power  = 108MW   (2,593MWhrs / 24hrs)

 3. Required Wind Plant Power= 360MW   (108MW / 0.30)

 4. Build Cost of Wind Power = $0.81 billion  (360MW x ($2,250,000 per MW) )

 5. Cost of Pumped Storage = $0.0 billion

Cost for building the same capacity to produce 2,593MWhrs of wind energy per day, without pumped storage = $0.81 billion.


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